In the development of sanitary fixtures, such as shower receptors, spas, bathtubs, sinks, lavatories and the like, the traditional porcelain-cast iron fixtures have gradually been replaced by lighter and more resilient composite structure. A common practice in the composite manufacture is to combine the thermoplastic and thermosetting materials in finishing products. The thermoplastic materials are typically in a sheet form and can be shaped into the final profile by vacuum forming. The thermoplastic material provides the cosmetic surface of the finishing product. The thermosetting materials are typically glass fiber reinforced unsaturated polyester resins. The thermosetting materials provide structure strength for the finished product after curing. The thermosetting material may also contain inserts for additional structure strength. European Patent No. EP 002,953 describes a reinforced plastics article which comprises a layer of plastic material bonded to fibrous reinforcement, where the reinforcement may comprise a laminate of continuous strand glass fiber mat between chopped strand glass fiber mats bonded together by cured thermosetting polymer. Great Britain Patent No. GB 2,087,295 describes a close-molding process to produce the shell-like receptacle.
Although the manufacture of sanitary fixtures employs most applications for the thermoplastic/thermosetting composites, the same type of composite construction can be found in the applications of other fields. U.S. Pat. No. 4,082,882 describes a structural sandwich by combining acrylic sheet, glass fiber reinforced unsaturated polyester resin, and plywood. U.S. Patent Publication No. 2004/0146714 describes a composite construction, such as a boat hull, comprising a thermoplastic layer and a fiber glass reinforcement composite. The thermoplastic layer comprises an acrylic film having a thickness of 0.5 to 1.5 mm and an ABS layer having a thickness of 0.5 to 15 mm. Applications of thermoplastic/thermosetting composites also can be found in transportation and construction areas.
The bonding between the thermoplastic and thermosetting materials is critical for the structure integrity of the composites. Delamination between the thermoplastic and thermosetting material in composites will decrease structural strength and can result in part failure. Weak bonding between the thermoplastic and thermosetting materials may also cause blistering when the composite is submerged in water for a long period of time. Much research has been conducted to improve the adhesion of thermoplastic and thermosetting materials. The thermosetting materials also may contain fillers and other additives for ways to improve the bond between thermoplastic and thermosetting materials.
U.S. Pat. Nos. 3,582,388 and 3,707,434 describe a method for the production of rigidified plastic laminates based on acrylonitrile-butadiene-styrene (ABS) resins and acrylic resins. The ABS or acrylic sheet was less than 0.2 inch in thickness and was vacuum-formed into the final shape of article then a glass fiber reinforced unsaturated polyester resin was bonded to the plastic sheet to form the final composites. The unsaturated polyester resin contains inert organic solvent and particles for improving the bonding and stress distribution from shrinkage occurred during the cure of unsaturated polyester resin.
U.S. Pat. No. 3,720,540 uses bond-improving additives consisting of a monomeric styrene compound and chalk or talc in the thermosetting unsaturated resin to improve the bond between thermosetting material and the thermoplastic substrate, particularly when the substrate is made of acrylic or ABS material. Great Britain Patent No. GB 2,114,466 describes a process using an unsaturated polyester resin composition incorporating a blowing agent and hollow glass microspheres for promoting the bonding to the acrylic sheet. The hollow microspheres also reduce the density of the material. U.S. Pat. No. 4,844,944 uses isocyanate-modified thermosetting unsaturated mixture of polyester and polyether dense foam resin substrate layer to become bonded to the thermoplastic layer through chemical linkages. European Patent No. EP 528,788 bonds the thermoplastic shell to the fiber reinforced resin layer by a silane-based coupler. The thermosetting resin includes at least one component selected from the groups of polyester, epoxy, acrylic, vinyl esters and the blends thereof, but does not contain isocyanate.
The adhesion between polymeric substrates can be imparted by surface treatment or surface modification. U.S. Pat. No. 5,755,913 uses surface graft copolymerization to introduce functional groups which are able to undergo free radical initiated polymerization onto both polymeric surfaces. Both polymeric substrates are then brought together with the modified surfaces contact each other in the presence of liquid medium. The bonding is achieved after the liquid medium substantially dries. U.S. Patent Publication No. 2003/0090023 improves adhesion between the insert material and the base resin by coating an insert material with primer and coating surface of the primer with dope cement. The dope cement was obtained by dissolving a synthetic resin, which is compatible to the base resin, in a solvent.
Japanese Patent No. JP 49006063 describes a process to improve the bonding strength by first coating molded ABS with an acrylic polymer then laminating the body with glass mat impregnated with an unsaturated polyester or an epoxy resin. The ABS coated with an acrylic polymer is stored 24 hours at room temperature before laminated with the unsaturated polyester-impregnated glass mat. The laminated composite is stored at room temperature for 5 hours and post-cured at 60° C. for another 4 to 5 hours. This part is then stored at room temperature for another 24 hours to give a superior bonding strength compared to the part without acrylic polymer coating on ABS.
Treatment of bonded polymeric materials at the elevated temperature was used for improving the adhesion of thermoplastic materials. U.S. Pat. No. 7,033,458 improves adhesion between two adjacent layers of a laminate membrane by annealing the laminate membrane at a temperature between an α-transition temperature and a β-transition temperature of at least one polymeric component for a period of time. The adhesion improvement is accomplished through diffusion of polymeric components.
U.S. Pat. No. 7,135,233 describes a multi-layer composite structure having improved weatherability and adhesion to fiber-reinforced plastic substrate. The multi-layer composites have an outer layer of UV stabilized acrylic, a second layer of acrylate-modified acrylonitrile-styrene-acrylate rubber (ASA), a third layer of modified ABS with decreasing softening on contact with styrene, and optionally a fourth layer of polyacrylate. It is believed that the improved adhesion arises from decreased softening of the ABS by the resin of the fiberglass.
Depending on the type of thermoplastic material used in the manufacture of thermoplastic/thermosetting composites, the selection of thermosetting material is significantly influenced by adhesion consideration. Unsaturated polyester and vinyl ester resins are most commonly used for backing acrylic and ABS thermoplastic sheets. It is well known that not all types of unsaturated polyester and vinyl ester resins adhere to all types of acrylics. The thermosetting resin can be used unfilled or filled for the application. The advantage of using the filled resin is that the raw material manufacturing costs are lower. However, the addition of filler may also impact the adhesion between the thermoplastic and thermosetting materials. As a result, the adhesion issue limits the selection of thermosetting resins as well as the thermoplastic material for the construction of composites laminate.
The present invention improves the adhesion between a thermosetting laminate and a thermoplastic shell by post-curing the finished composites at elevated temperature. With this invention, no special surface treatment is needed for the surface of thermoplastic shell and various types of thermosetting resins, including high DCPD type unsaturated polyester resins, can be used in making reinforced plastic laminates. The present invention enables the manufacturer to expand the material selection for the construction of composites for various applications. A carefully designed process may also speed up the production of composites. The production costs can be lower through the combination of lower material costs and faster processing time. Another added benefit for present invention is that it allows the composite manufacturer to use MACT compliant thermosetting resins, which will reduce the volatile organic compound (VOC) emission if the laminate is made through an open molding process.